1. Field of the Invention
The present invention relates to phosphates, and in particular relates to curing agents of phosphorous containing phenol novolac resins, methods for manufacturing the same, and compositions including the same.
2. Description of the Related Art
Flame retardants can be classified into two major types: an organic type and an inorganic type. A high amount of the inorganic flame retardant is added to a resin for flame retardation effect; however, an overly high additive amount of the inorganic flame retardant contrarily degrades physical properties of the resin. The organic flame retardant can be further classified into a halogen containing group and a phosphorous containing group. The halogen containing flame retardant produces hydrogen halide and a lot of smoke while burning and therefore is harmful for human beings. Accordingly, the phosphorous containing flame retardant is the main type used for developing organic flame retardants.
The flame retardation effect of the phosphorous containing flame retardant depends on the phosphorous amount of phosphide. In addition, the flame retardant in the resin will be exposed to a high temperature when the resin is compression-molded. As such, developing a phosphide containing a high phosphorous amount with excellent thermal stability is necessary.
In the past, typical phosphorous containing flame retardants were of a monomer type such as triphenyl phosphate (TPP) or trucresyl phosphate (TCP). Because monomer has low molecular weight, it easily vaporizes when in use. A condensed phosphoric ester, including a very low amount of volatile component, has been developed to overcome the vaporization defect. See U.S. Pat. Nos. 6,319,432, 6,605,736, 6,605,737, and 6,613,928.
A phenol novolac resin inherently has excellent properties such as low cost, high thermal resistance, high water resistance, high electrical insulation, high corrosion resistance, high mechanical strength, good adhesion, and low smoke generation. Components of the phenol novolac resin can be tuned in different amounts to obtain a modified phenol novolac resin with different properties. The modified phenol novolac resin is widely applied in molding materials, gelling adhesives, or coatings. If the phosphorous is combined with the phenol novolac resin, a product thereof will have the inherent advantages of the phenol novolac resin, a high phosphorous amount, and excellent flame retardation effect. The conventional modified phenol novolac resins containing phosphorous are obtained by combining DOPO and the phenol novolac resin. See Journal of Applied Polymer Science, Vol. 78, 1636-1644 (2000), Polymer 42(2001) 7617-7625, and U.S. Pat. Nos. 6,291,626, 6,613,848, 6,797,821, 6,992,151, and 7,064,157.